Regioselective Borylation of the C鈥揌 Bonds in Alkylamines and Alkyl Ethers. Observation and Origin of High Reactivity of Primary C鈥揌 Bonds Beta to Nitrogen and Oxygen

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• 作者：Qian Li ; Carl W. Liskey ; John F. Hartwig
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：June 18, 2014
• 年：2014
• 卷：136
• 期：24
• 页码：8755-8765
• 全文大小：854K
• 年卷期：v.136,no.24(June 18, 2014)
• ISSN：1520-5126

文摘

Borylation of aliphatic C鈥揌 bonds in alkylamines and alkyl ethers to form primary aminoalkyl and alkoxyalkyl boronate esters and studies on the origin of the regioselectivity of these reactions are reported. The products of these reactions can be used directly in Suzuki鈥揗iyaura cross-coupling reactions or isolated as air-stable potassium trifluoroborate salts. Selective borylation of the terminal C鈥揌 bond at the positions 尾 to oxygen and nitrogen occurs in preference to borylation of the other terminal C鈥揌 bonds. Experimental studies and computational results show that C鈥揌 bond cleavage is the rate-determining step of the current borylation reactions. The observed higher reactivity of C鈥揌 bonds at the terminal position of ethylamines and ethers results from a combination of attractive Lewis acid鈥揵ase and hydrogen-bonding interactions, as well as typical repulsive steric interactions, in the transition state. In this transition state, the heteroatom lies directly above the boron atom of one boryl ligand, creating a stabilizing interaction between the weak Lewis acid and Lewis base, and a series of C鈥揌 bonds of the substrate lie near the oxygen atoms of the boryl ligands, participating in a set of weak C鈥揌路路路O interactions that lead to significant stabilization of the transition state forming the major product.